Wednesday, August 3, 2011

Dancing Squid

Ed Yong tweeted a video last week on twitter, and the video went viral. A little surfing brought me another video, this time the entire process of decimating the poor cephalopod, from fishing to killing and finally, consumed.

Image: theawesomer.com

Yeah it freaked me out too.

A little while later someone posted an explanation for the phenomenon:When a creature dies, its neurons don’t stop working right away. So long as there is still enough energy around to maintain that membrane potential, the neurons will work.
What you might have noticed is that in the case of the dancing dead, the cooks have added one key ingredient: salt (soy sauce is very salty). Salt – or sodium chloride – is chock full of sodium ions. This overwhelming dose of sodium ions is enough to trigger the still-working neurons into firing, signalling the muscles to contract.--Christie Wilcox

A close up image of octopus arms showing suction cups. Image: seasky.org

Looking at the struggling squid, I felt like someone pouring soy sauce over a fresh wound on me. Ouchhhh!

Death is a notoriously difficult term to define, and we're not entirely sure whether the squid in the video was already dead when poured with the soy sauce-cephalopods like octopus can live out of water for 30~60minutes. So for the sake of brevity, let us just assume that it was already dead by the time it's mantle was cut.

Remember that some actions, for example pulling your hands away from a hot kettle, need not go through the brain--the pain receptor sends an impulse to our spinal cord, where they are transferred to motor neurons that are connected to the muscles in our arms, which are then stimulated to contract and pull the hand away. This is called somatic reflex.

Image: education.vetmed.vt.edu

The octopus, which has the most advanced nervous system of any invertebrates, has arms several hundred times more sensitive than ours. In fact a new research suggests that cephalopods, for example octopuses, allocate some of the motor control to neural circuitry embedded in the arms themselves, instead of relying on the brain alone.

If you've got enough experience in cooking, you'd probably know that frozen octopus arms, even those that had been dead for more than a day, could still move-albeit just a little bit-when you pour hot water over it.
Hence, if the squid had in fact died, what we saw in the video was not an actual "pain" response from the it's brain, but rather a natural response from the neurons that didn't "die" fast enough, and thus responded to the pouring of the soy sauce.